1. Field of the Invention
The invention relates to the field of seismic data processing. In particular, the invention relates to systems, program products, and related methods for suppressing undesirable energy, particularly in the form of residual water bottom energy, in seismic data.
2. Description of Related Art
Seismic reflections/refraction data can be collected in marine environments with a receiver array deployed on the sea floor. Such data retrieval systems, however, record, along with the usable data, a significant amount of energy that is trapped in the water layer. This energy infects the entire seismic section by following each and every recorded signal from deeper events. This unwanted energy is typically very high amplitude relative to the recorded reflections. Another term for this effect, which originates from the nature of the energy itself, is “ghost” energy. That is, as good seismic signals are recorded, they are followed by water bottom signals in a ghost like fashion. These ghost events may constructively combine to the point where the desired reservoir signals are nearly undetectable. In marine surveys using ocean bottom cables, in particular, energy trapped in the water layer is recorded, at least in part, due to the position of the cable on the sea bottom. This unwanted energy is typically very high amplitude relative to the recorded reflections. During early surveys of this type, these high amplitude levels could not be addressed by industry standard single channel gapped deconvolution. This limited the use of ocean bottom cable acquisition to only the most of shallow of water depths as this tends to cancel trapped water bottom energy.
The same issue has caused ocean bottom cable systems to evolve over the past 20 years. State-of-the-art seismic data collection and processing systems have evolved to try to deal with this issue. For a combination of reasons, these systems do not completely suppress ghost energy. Modern cable configurations have at least two sensors, a hydrophone and a velocity phone, which record desired reflection signals at one polarity and undesired water bottom energy at opposite polarities. Upon summing these two sensors, ideally the water bottom energy cancels and the desired signals reinforce. This dual sensor design allows cables to be deployed to deeper water depths, which is a great advance for the industry as it allow acquisition in areas deep water vessels could not previously access. Unfortunately, the efficiency of that summation process is dependent on a number of factors. These factors include how well coupled the cable is to the sea bottom, what type of sediments the cable rests in, and how rugged the sea bottom topography is. Prior to summation, several industry standard processing steps occur to combat these issues. They include scaling, noise removal, and wave field separation, to name a few. All of these steps target the water bottom energy, but do not completely suppress it. To make matters worse, the residual levels may vary across a project, depending on the efficiency of the summation.
Industry standard pre-stack processing techniques, including surface consistent deconvolution in the source, receiver, mid-point, and offset domain, have been employed to target this energy. Such techniques, however, do not provide a measure of the residual water bottom energy left in the data. These unknown, spatially variable energy signals eventually cause an interpreter of the data to lose confidence in the seismic data as it will not be clear if observed variable amplitudes are due to residual water bottom energy or important lithologic characteristics of the reservoir.
Industry standard, post-stack, single channel, deconvolution has also been employed. Such post-stack, single channel, deconvolution is normally applied on stack data to attenuate reverberation effects such as residual water bottom energy. In such techniques, an autocorrelation calculated from a window of data on the stacked seismic trace, sometimes mixed with one or two neighboring traces, is typically used in a standard predictive deconvolution (e.g., Weiner-Levinson) algorithm to obtain a causal inverse filter which is applied to the data. Recognized by the inventors, however, is that as residual water bottom amplitude levels change across the prospect area, sometimes above and sometimes below recorded signal and background noise levels, industry standard techniques based on a single autocorrelation have a difficult time distinguishing residual water bottom energy from other desired events that may have a reverberatory signature, such as periodic geological reflectors. The result is a sub-optimum suppression of undesired water bottom energy along with a potential suppression of desired signals.
Accordingly, recognized by inventors is that deficiencies of prior systems and techniques/methodologies include improper summation of dual sensor ocean bottom cable data, inefficient pre-stack or post-stack predictive deconvolution operator design, and a lack of quality control plots that locate problem areas or measure residual amplitude levels in the data. These deficiencies lead to variable levels of residual water bottom energy in the data that reduce its resolving power and interpretability.
Thus, recognized by inventors is the need for a system, program product, and computer implemented methods which can efficiently find and suppress residual water bottom energy from seismic data volumes, thereby effectively increasing the resolving power of seismic data—thus, leading to an improved interpretation of seismic signals reflected from oil reservoirs. Further, recognized is the need for a cost effective system, program product, and computer implemented methods that effectively identify residual multiple energy which only require stack data, and thus, can be executed on desktop workstations, rather than an enormous computer system, as is generally required by multi-channel industry techniques/methodologies which rely on pre-stack data.
Also, recognized by inventors is the need for an improved system, program product, and computer implemented methods which implement a multi-channel post-stack deconvolution that leverages redundancy in sub-line, cross-line, and water bottom time domains to arrive at efficient predictive deconvolution operators for the seismic data, and which provide efficient quality control plots to allow a user to spatially analyze the levels of residual water bottom energy in the seismic data. Recognized is that by efficiently suppressing side lobes on reflection events caused by residual water bottom energy, such system, program product, and methods can create a seismic volume that has a higher resolving power. The transformation of raw seismic data into seismic data with a substantially higher resolving power would provide a significant benefit to a seismic data interpreter using the seismic data to estimate reservoir properties and guide horizontal drilling campaigns.